In many pipelines where flowing gaseous or liquid products are handled and controlled, it is necessary to accomplish a wide variety of fluid measurement during the various aspects of fluid processing. Typical fluid measurements include measurement of the pressure of the fluid and measurement of the volume of fluid flowing at any given time. In many cases, it is also desirable to take periodic samples of the flowing fluid to insure that processing personnel remain continuously aware of the various characteristics of the fluid and any changes that may occur as the fluid is processed. From the standpoint of sampling, in many cases it is desirable to frequently sample process fluid that is contained within a process vessel other than a pipeline. It is desirable, therefore, to provide means for extacting measured quantities of fluid from process vessels in simple and efficient manner. It is also desirable to insure that the sample extracting apparatus be capable of being separated from the process vessel or pipeline without requiring shutting down of the process involved.
It is well known that liquid products contained within process vessels or flowing through pipelines tend to stratify based on the weight of the molecules from which the process fluid is composed. Accordingly, heavier molecules settle to the bottom of the pipeline or process vessel and lighter molecules tend to rise to the upper portion of the fluid. If a fluid sample is taken from the upper most or lower most parts of the pipline or process vessel, the sample so taken may not be truly representative of the average nature of the fluid product involved. For example, in the event the fluid is a hydrocarbon product, the upper portion of the process vessel or pipeline may tend toward the lighter ends of the hydrocarbon product. Conversely, a sampler positioned with its inlet at the very bottom of the pipe may tend to distort the data by yielding a sample having a larger number of heavy molecules. It is desirable, therefore, to provide sampling apparatus that is enabled to take samples from the central portion of the pipeline or process vessel to thereby insure that the sample accurately conforms to the average of the process fluid.
From the standpoint of taking samples from pipelines, it should be borne in mind that it is typical, in many cases, to pass pipelines pigs or scrapers through the pipe to remove accumulation of material adhering thereto. In the event a pipeline sampling device extends into the pipe, it would interefere with passage of the pig or scaper. It is, therefore, desirable to provide a sampling device that may be utilized in conjuction with pipelines and which has the capability of being retracted from the flow way of the pipeline under circumstances where pigs, scrapers or other devices are passed through the pipe for cleaning or other servicing operations. It is also desirable that the sampling device be capable of being retracted from the flow way of the pipe without requiring the fluid processing system to be shut down.
In many cases, process piping is of quite small dimension. Even though sampling probes or transducers may be of relatively small dimension, the probe apparatus may create substantial interference with the flowing fluid when emplaced within the flow way of small pipes. It is, therefore, desirable to provide a fluid sampling transducer having the inlet thereof located at the free extremity of the transducer so that only a small portion of the transducer is positioned in the flowing fluid. In the apparatus of this invention only, the free extremity of the probe need be positioned near the center of the flow way in order to achieve optimum sampling and yet the transducer does not interfere materially with the flow of fluid.